Multi-zone resistive heater

ABSTRACT

A heating apparatus including a stage comprising a surface having an area to support a wafer and a body, a shaft coupled to the stage, and a first and a second heating element. The first heating element is disposed within a first plane of the body of the stage. The second heating element is disposed within a second plane of the body of the stage at a greater distance from the surface of the stage than the first heating element. A reactor comprising a chamber, a resistive heater, a first temperature sensor, and a second temperature sensor. A resistive heating system for a chemical vapor deposition apparatus comprising a resistive heater. A method of controlling the temperature in a reactor comprising providing a resistive heater in a chamber of a reactor, measuring the temperature with at least two temperature sensors, and controlling the temperature in the reactor by regulating a power supply to the first heating element and the second heating element according to the temperature measured by the first temperature sensor and the second temperature sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to heating mechanisms for process chambers,particularly, heating mechanisms for chemical vapor deposition chambers.

2. Description of Related Art

Chemical vapor deposition (CVD) is a popular process for depositingvarious types of films on substrates and is used extensively in themanufacture of semiconductor-based integrated circuits such as, forexample, the processing of semiconductor wafers to form individualintegrated circuit device. In typical CVD processing, a wafer or wafersare placed in a deposition or reaction chamber and reactant gases areintroduced into the chamber and are decomposed and reacted at a heatedsurface to form a thin film on the wafer or wafers.

In general, there are single-wafer and multi-wafer CVD reaction chambersin use today. Multi-wafer reaction chambers typically resemble verticalfurnaces capable of holding, for example, 25 wafers or more. For lowpressure CVD (LPCVD), for example, 0.25-2.0 torr, for the deposition ofSi₃N₄ or polysilicon, a typical deposition time for a multi-waferchamber might be several hours. Si₃N₄, for example, is formed at atemperature between 700-800° C. and a deposition time of 4-5 hoursdepending upon layer thickness in a multi-wafer chamber.

A second type of CVD reaction chamber is a single-wafer chamber in whicha wafer is supported in the chamber by a stage or susceptor. Thesusceptor may rotate during the reaction process. For an LPCVD Si₃N₄deposition, for example, a suitable layer thickness may be produced at700-800° C. in about two minutes.

In general, there are two types of heating schemes used in CVD systems:resistive heating schemes that utilize a resistive heating elementlocalized at the wafer, and radiant heating schemes that use a radiantheating element such as a lamp or lamps usually placed outside thereaction chamber. Resistive heating schemes in a single-wafer chambergenerally incorporate the resistive heating element directly in thestage or susceptor that supports the wafer in the chamber. In thismanner, the reaction produced during the deposition may be generallymore localized at the wafer.

In single-wafer resistive heating schemes that utilize a heating elementwithin a stage or susceptor that supports a wafer, the heating elementis typically a thin layer of conductive material, such as a thin coiledlayer (about 2 mils) of a molybdenum (Mo) material formed in a singleplane of the body of the susceptor. This design may be described as a“single-zone resistive heater,” the “zone” description referring to thelocation of the heating element in a single plane in the body of thestage or susceptor. The CVD reaction in which the resistive heaters areused typically has a temperature compatibility to approximately 550° C.At higher temperatures, temperature uniformity becomes problematic. Onereason is that heat loss in a resistive heater increases with highertemperatures, particularly at the edges of the stage or susceptor.Single-zone resistive heaters typically do not have the ability tocompensate for differences in heat loss across the stage or susceptor.The pressure in a chamber will also modify the temperature stability ofsingle-zone resistive heaters.

In addition to providing the requisite temperature, the resistiveheating element must also be amenable to the chemical environment in thereaction chamber including high temperature and chemical species. Onesolution to the compatibility consideration in prior art single-zoneresistive heaters is to form the susceptor of aluminum nitride (AlN)with the heating element formed inside the susceptor.

Radiant heating schemes generally position lamps behind heat-resistantprotective glass or quartz in the reaction chamber. Since the entirechamber is heated by the lamps, the CVD reaction occurs throughout thechamber.

Radiant or lamp heating schemes offer the benefit of generating a highchamber temperature and controlling that temperature better thanresistive heating schemes. However, since radiant heating schemesutilize heating elements, e.g., lamps, placed outside of the reactionchamber, the ability to control the temperature in the chamber becomesmore difficult as the chamber walls become coated with chemicals orother materials or reaction products used in the reaction chamber. Thus,as the materials used in the chamber deposit on the chamber glass orquartz, for example, the effectiveness of the heating is reduced and theprocess performance is effected.

In this regard, a reaction chamber used in a radiant heating scheme mustbe cleaned often. A typical cleaning agent is nitrogen trifluoride(NF₃). In Si₃N₄ CVD processes, for example, Si₃N₄ reaction products formon the chamber walls and other components inside the chamber, such as aquartz window(s). Si₃N₄ is difficult to clean from a reaction chamberwith a cleaning agent like NF₃. The cleaning temperature generally mustbe high in order to dissociate the NF₃ and provide enough thermal energyto clean Si₃N₄. If the cleaning temperature is high, the NF₃ will alsoattack components in the chamber, such as the susceptor. A remote plasmasource used to energize the NF₃ can reduce the cleaning temperature butactivated NF₃ species (particularly radicals) tend to attack quartzcomponents. Therefore, currently there is no effective cleaning solutionfor radiant-based chambers. Since the walls of the reaction chamber arenot easily cleaned with NF₃, Si₃N₄ material accumulates and shortens thelifetime of the chamber.

In LPCVD reactions, temperature uniformity is generally important. Thesurface reaction associated with a CVD process can generally be modeledby a thermally activated phenomenon that proceeds at a rate, R, given bythe equation:

R=R_(o)e^([−E) _(^(a)) ^(/kT])

where R_(o) is the frequency factor, E_(a) is the activation energy inelectron volts (eV), and T is the temperature in degrees Kelvin.According to this equation, the surface reaction rate increases withincreasing temperature. In a LPCVD process such as a Si₃N₄ deposition,the activation energy (E_(a)) is generally very high, on the order of0.9-1.3 eV. Accordingly, to obtain a uniform thickness across the wafer,the temperature uniformity across the wafer should be tightlycontrolled, preferably on the order of ±2.5° C. or less for temperaturesaround 750° C.

Prior art single-wafer radiant heating schemes offer acceptabletemperature uniformity even at higher temperatures (e.g., 750° C.) whenthe chamber is clean. However, as materials accumulate on the walls ofthe chamber, temperature uniformity becomes difficult.

It is also difficult to obtain a uniform high temperature (e.g.,700-750° C.) across a wafer with a single-zone resistive heater. Asnoted, in general, heat loss is not uniform across the surface of asusceptor at higher temperatures. A single-zone heater cannotcompensate, for example, for a greater heat loss toward the edges of thesusceptor than at its center. Thus, temperature uniformity is a problem.

A second problem with single-zone resistive heaters such as describedabove and temperatures of 750° C. is problems associated with localizedheating. At high temperatures, single-zone heaters exhibit concentratedlocalized heating associated with high density power applied to theheating element at a localized area. Consequently, temperatureuniformity is affected. A third problem with single-zone resistiveheaters is that variations in manufacturing of the heating element cancause fluctuations in performance of a heating element which can lead tonon-uniformity. The single-zone heater cannot be adjusted to compensatefor the manufacturing variation. Further, at high temperature operation,single-zone heaters have shorter lifetimes due to the high power densityapplied at the power terminals and to the heating elements.

Still further, prior art resistive heaters and chambers that providesuch heaters offer limited dynamic temperature measurement. In general,the only dynamic temperature measurement (i.e., real-time temperaturemeasurement) is provided by a thermocouple placed generally at thecenter of the susceptor at a point below the surface of the susceptor.The temperature measurement (such as by a thermocouple) may provide anaccurate temperature measurement of the temperature at the center of thesusceptor, but cannot provide any information about the temperature atthe edges of the susceptor. Thermal cameras that view the temperaturewithin the chamber from a vantage point outside the chamber have beenemployed but generally only offer static information about thetemperature in the chamber. Any changes to the chamber pressureassociated with adjusting the CVD process recipe also tend to play arole in the ability to control the reaction temperature in the chamber.Thus, single-zone resistive heating schemes are generally limited tooperating at one particular temperature and pressure. Changes to eitherthe chamber temperature or the chamber pressure negatively effect thetemperature uniformity. Thus, such single-zone-heating schemes areinadequate for high temperature CVD processes.

What is needed is a reaction chamber and a heating scheme for a reactionchamber compatible with high temperature operation, e.g., on the orderof 700° C. or greater, that is chemically resistant to the elements andachieves high temperature uniformity localized at a reaction site.

SUMMARY OF THE INVENTION

A heating apparatus is disclosed. In one embodiment, the heatingapparatus includes a stage or susceptor comprising a surface having anarea to support a wafer and a body, a shaft coupled to the stage, and afirst and a second heating element. The first heating element isdisposed within a first plane of the body of the stage. The secondheating element is disposed within a second plane of the body of thestage at a greater distance from the surface of the stage than the firstheating elements. According to this embodiment, a multi-zone heatingapparatus is disclosed defined by the first and second heating element.In this manner, the invention allows individual control of at least twodistinct heating zones of a stage thus increasing the temperaturecontrol and temperature uniformity of the stage as compared to prior artsingle-zone heating apparatuses.

In one aspect, the heating apparatus is a resistive heater capable ofoperating at high temperatures and providing enhanced temperatureuniformity over single-zone resistive heaters. Each heating element maybe separately controlled to maintain a collectively uniform temperatureacross the surface of the stage. For example, in the situation whereheat loss is greater at certain areas of the stage, heating zonesassociated with those areas may be supplied with more resistive heat tomaintain a chosen operating temperature despite the heat loss. One waythis is accomplished is by varying the resistance of a multiple heatingelements across an area of the stage. Where, for example, heat lossthrough the shaft is determined to be greater than the heat loss atother areas of the stage, the resistance of one heating element in areaof the stage corresponding with (e.g., over) the shaft is increased.Similarly, where heat loss at the edge at other area of the stage isdetermined to be greater than the heat loss at other areas, theresistance of one heating element in an area corresponding with the edgearea of the stage is increased.

Also disclosed is a reactor comprising, in one embodiment a chamber anda resistive heater. The resistive heater includes a stage disposedwithin the chamber including a surface having an area to support a waferand a body, a shaft coupled to a stage, a first heating element disposedwithin a first plane of the body of the stage, and a second heatingelement disposed within a second plane of the body of the stage. In oneaspect, the power density of the first heating element is greater thanthe power density of the second heating element in an area correspondingwith a first portion of the stage area. At the same time, the powerdensity of the first heating element is less than the power density ofthe second heating element in an area corresponding with a secondportion of the stage area.

As described, the reactor of the invention provides a multi-zoneresistive heater, such as a single-wafer heater, including at least tworesistive heating elements disposed within separate planes of a stage orsusceptor. The distinct heating elements allow, in one instance,separate areas of the stage to be individually regulated by varying thepower density of the individual heating elements in different areas ofthe stage. In one embodiment, by placing the first heating element at aposition closer to the surface of the stage than the second heatingelement, a greater power density can be supplied to the second heatingelement to account for greater heat losses at areas associated with theedge of the stage while minimizing potential localized “hot spots”associated with the greater power density. Multiple temperature sensorsassociated with one embodiment of the reactor offer the opportunity tomore uniformly control the temperature of the resistive heater thanprior art reactors having only a single thermocouple in the center ofthe susceptor.

A resistive heating system for a chemical vapor deposition apparatus isfurther disclosed. The heating system includes, in one embodiment, aresistive heater comprising a stage including a surface having an areato support a wafer and a body, a shaft coupled to the stage, a firstheating element, and a second heating element disposed within distinctplanes of the body of the stage. The heating system of the inventionprovides a multi-zone resistive heater with at least two distinctheating elements to control the temperature of the heater which improvesthe temperature uniformity in, for example, a high-temperature CVDprocess, including process conditions operated at temperature in excessof 700° C. (e.g., LPCVD)

A method of controlling the temperature in the reactor is still furtherdisclosed. In one embodiment, the method comprises supplying a power toa first resistive heating element disposed within a first plane of thebody of a stage of a resistive heater and a second resistive heatingelement disposed within a second plane of the body of the stage. Themethod also comprises varying a resistance of at least one of the firstresistive heating element and the second resistive heating elements inat least two areas of the stage.

Additional embodiments of the apparatus, the reactor, the heatingsystem, and the method of the invention, along with other features andbenefits of the invention are described in the figures, detaileddescription, and claims set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of the CVD system showing theheater inside a reaction chamber in a “wafer-process” configuration inaccordance with an embodiment of the invention.

FIG. 2 is a cross-sectional side view of the CVD system of FIG. 1showing a heater inside a reactor chamber in a “wafer-separate”configuration in accordance with an embodiment of the invention.

FIG. 3 is a cross-sectional side view of the CVD system of FIG. 1showing a heater inside a reactor chamber in a “wafer-load”configuration in accordance with an embodiment of the invention.

FIG. 4 is an expanded one-half cross-sectional view of a portion of theheater portion of the CVD system in accordance with an embodiment of theinvention.

FIG. 5 is a bottom view of the heater of the CVD system taken inaccordance with an embodiment of the invention.

FIG. 6 is a top view of the stage or susceptor of the heater of the CVDsystem taken through line A—A of FIG. 4 in accordance with an embodimentof the invention.

FIG. 7 is a top view of the stage or susceptor of the heater of the CVDsystem taken through line B—B of FIG. 4 in accordance with an embodimentof the invention.

FIG. 8 is a top schematic view of the stage or susceptor of the heaterof the CVD system showing three zones in accordance with an embodimentof the invention.

FIG. 9 is a graphical representation of the power ratio versus the stageor susceptor radius of a heater in accordance with an embodiment of theinvention.

FIG. 10 is an expanded cross-sectional view of a portion of the CVDsystem showing two pyrometers coupled to a top portion of the chamberwall in accordance with an embodiment of the invention.

FIG. 11 is a top view of the chamber of the CVD system showing twopyrometers above respective heating zones in accordance with anembodiment of the invention.

FIG. 12 is a flow chart of a method of processing a wafer in a CVDchamber according to an embodiment of the invention.

FIG. 13 is a block diagram of an embodiment of the system of theinvention having a controller to control the power supplied to heatingelements of the heater.

DETAILED DESCRIPTION OF THE INVENTION

The invention generally relates to embodiments of a heating apparatus, areactor, a heating system for a chemical vapor deposition apparatus, anda method of controlling the temperature in the reactor. In one aspect,the invention utilizes a heating apparatus suitable for supporting asingle-wafer (e.g., a semiconductor wafer) on a stage or susceptor in areaction chamber. The heating apparatus includes at least two heatingelements to maintain a uniform reaction temperature of the surface ofthe susceptor (and of a wafer on a susceptor). In one embodiment, eachheating element lies in a distinct plane in the susceptor of the heater.Each heating element is coupled, in one embodiment, to a power sourceand the resistance of each heating element is varied across an area ofthe stage. The temperature associated with different areas of thesurface of the susceptor or at the wafer may be measured and the heatingelements controlled. By controlling the individual heating elements ofthe heating apparatus, factors such as heat loss and pressure changes inthe reactor are accommodated and improved temperature uniformity isachieved even at temperatures greater than 700° C. Thus, a heatingapparatus having multiple heating elements (e.g., a multi-zone heater)provides a useful heating element for a CVD reactor or system and hightemperature LPCVD processes that are preferred in the deposition ofSi₃N₄ and polysilicon deposition.

FIG. 1, FIG. 2 and FIG. 3 show cross-sectional views of a portion of asystem incorporating a reactor according to an embodiment of theinvention. Such a system is used, for example, in a CVD process,including an LPCVD process for the deposition of Si₃N₄ or polysiliconfilms on a wafer or substrate.

FIG. 1 illustrates the inside of process chamber body 100 in a“wafer-process” position. FIG. 2 shows the same view of the chamber in a“wafer-separate” position. Finally, FIG. 3 shows the samecross-sectional side view of the chamber in a “wafer-load” position.

FIG. 1, FIG. 2 and FIG. 3 show chamber body 100 that defines reactionchamber 145 where the reaction between a process gas or gases and thewafer takes place, e.g., a CVD reaction. Chamber body 100 isconstructed, in one embodiment, of aluminum and has passages 102 forwater to be pumped therethrough to cool chamber body 100 (e.g., a“cold-wall” reaction chamber). Resident in chamber 145 is resistiveheater 150 including, in this view, susceptor 155 supported by shaft158. In one embodiment, susceptor 155 has a surface area sufficient tosupport a semiconductor wafer. A cynlindrical susceptor having adiameter of approximately 9.33 inches supported by a shaft having alength of approximately 10 inches is suitable to support an eight inchdiameter wafer.

Process gas enters otherwise sealed chamber 145 through opening 175 in atop surface of chamber lid 170 of chamber body 100. The process gas isdistributed throughout chamber 145 by perforated face plate 180 locatedin this view above resistive heater 150 and coupled to chamber lid 170inside chamber 145.

A wafer is placed in chamber 145 on susceptor 155 through entry port 105in a side portion of chamber body 100. To accommodate a wafer forprocessing, heater 150 is lowered so that the surface of susceptor 155is below entry port 105 as shown in FIG. 3. Typically by a robotictransfer mechanism, a wafer is loaded by way of, for example, a transferblade into chamber 145 onto the superior surface of susceptor 155. Onceloaded, entry port 105 is sealed and heater 150 is advanced in asuperior (e.g., upward) direction toward face plate 180 by lifterassembly 160 that is, for example, a step motor. The advancement stopswhen the wafer is a short distance (e.g., 400-700 mils) from face plate180. At this point, process gases controlled by a gas panel flow intothe chamber 145 through gas distribution port 175, through perforatedface plate 180, and typically react or are deposited on a wafer to forma film. In a pressure controlled system, the pressure in chamber 145 isestablished and maintained by a pressure regulator or regulators coupledto chamber 145. In one embodiment, for example, the pressure isestablished and maintained by baratome pressure regulator(s) coupled tochamber body 100 as known in the art.

After processing, residual process gas or gases are pumped from chamber145 through pumping plate 185 to a collection vessel. Chamber 145 maythen be purged, for example, with an inert gas, such as nitrogen. Afterprocessing and purging, heater 150 is advanced in an inferior direction(e.g., lowered) by lifter assembly 160 to the position shown in FIG. 2.As heater 150 is moved, lift pins 195, having an end extending throughopenings or throughbores in a surface of susceptor 155 and a second endextending in a cantilevered fashion from an inferior (e.g., lower)surface of susceptor 155, contact lift plate 190 positioned at the baseof chamber 145. As is illustrated in FIG. 2, in one embodiment, at thispoint, lift plate 190 does not advance from a wafer-load position to awafer-separate position as does heater 150. Instead, lift plate 190remains at a reference level, H₁, indicated in FIG. 2 on shaft 158. Asheater 150 continues to move in an inferior direction through the actionof lifter assembly 160, lift pins 195 remain stationary and ultimatelyextend above the superior or top surface of susceptor 155 to separate aprocessed wafer from the surface of susceptor 155.

Once a processed wafer is separated from the surface of susceptor 155, atransfer blade of a robotic mechanism is inserted through opening 105 toa “pick out” position inside chamber 145. The “pick out” position isbelow the processed wafer. Next, lifter assembly 160 inferiorly moves(e.g., lowers) lift plate 190 to, for example, a second reference level,H₂, indicated in FIG. 3 on shaft 158. By moving lift plate 190 in aninferior direction, lift pins 195 are also moved in an inferiordirection, until the underside of the processed wafer the surface oflift pin 195 contacts the transfer blade. The processed wafer is thenremoved through entry port 105 by, for example, a robotic transfermechanism that removes the wafer and transfers the wafer to the nextprocessing step. A second wafer may then be loaded into chamber 145. Thesteps described above are reversed to bring the wafer into a processposition. A detailed description of one suitable lifter assembly 160 isdescribed in U.S. Pat. No. 5,772,773, assigned to Applied Materials,Inc., of Santa Clara, Calif.

In high temperature operation, such as LPCVD processing of Si₃N₄ orpolysilicon, the reaction temperature inside chamber 145 can be as highas 750° C. or more. Accordingly, the exposed components in chamber 145must be compatible with such high temperature processing. Such materialsshould also be compatible with the process gases and other chemicals,such as cleaning chemicals, that may be introduced into chamber 145. Inone embodiment, exposed surfaces of heater 150 are comprised of aluminumnitride (AlN). For example, susceptor 155 and shaft 158 may be comprisedof similar aluminum nitride material. Alternatively, in a preferredconstruction, the surface of susceptor 155 is comprised of highthermally conductive aluminum nitride material (on the order of 95%purity with a thermal conductivity from 140 W/mK to 200 W/mK) whileshaft 158 is comprised of a lower thermally conductive aluminum nitride(on the order of 60 W/mK to 100 W/mK). Susceptor 155 of heater 150 istypically bonded to shaft 158 through diffusion bonding or brazing assuch coupling will similarly withstand the environment of chamber 145.

Lift pins 195 are also present in chamber 145 during processing.Accordingly, lift pins 195 must be compatible with the operatingconditions within chamber 145. A suitable material for lift pins 195includes, but is not limited to, sapphire or aluminum nitride. A furthercomponent that is exposed to the environment of chamber 145 is liftplate 190. Accordingly, in one embodiment, lift plate 190, including aportion of the shaft of lift plate 190, is comprised of an aluminumnitride (e.g., thermally conductive aluminum nitride on the order of 140W/mK to 200 W/mK) composition.

FIG. 1 also shows a cross-section of a portion of heater 150, includinga cross-section of the body of susceptor 155 and a cross-section ofshaft 158. In this illustration, FIG. 1 shows the body of susceptor 155having two heating elements, first heating element 250 and secondheating element 260. First heating element 250 and second heatingelement 260 are formed in distinct planes in the body of susceptor 155.For a susceptor having a thickness of approximately 0.68 inches (or1.728 cm), first heating element 250 is located approximately 5-8 mmfrom the surface of the susceptor. The significance of the location offirst heating element 250 relative to the surface of susceptor 155 willbe discussed below.

Each heating element (e.g., heating element 250 and heating element 260)is made of a material with thermal expansion properties similar to thematerial of the susceptor. One such material includes molybdenum (Mo),which has a thermal expansion coefficient similar to aluminum nitride.In one embodiment, each heating element includes a thin layer (e.g., 2mils) of molybdenum material in a coiled configuration.

In FIG. 1, second heating element 260 is formed in an inferiorly locatedplane of the body of susceptor 155 that is located inferiorly (relativeto the surface of susceptor 155) to first heating element 250. In oneembodiment, for a susceptor having a thickness of approximately 1.728cm, second heating element 260 is located in a plane approximately 5 mmfrom the plane of first heating element 250.

In this embodiment, first heating element 250 and second heating element260 are separately coupled to power terminals. The power terminalsextend in an inferior direction as conductive leads through alongitudinally extending opening through shaft 158 to a power sourcethat supplies the requisite energy to heat the surface of susceptor 155.

Also of note in the cross-section of heater 150 as shown in FIG. 1 isthe presence of thermocouple 210. Thermocouple 210 extends through thelongitudinally extending opening through shaft 158 to a point just belowthe superior or top surface of susceptor 155. In an embodiment wheresusceptor 155 is cylindrical, thermocouple 210 extends at a pointcorresponding approximately with the midpoint of the cylindrical body.

As noted above, the environment inside reactor 145 may be extreme formany materials. By locating thermocouple 210 as well as the conductiveleads to a power source, inside an opening in a reactor-compatible shaftand susceptor, concerns of degradation or decomposition of thesecomponents are alleviated as the components are not exposed to theenvironment of chamber 145.

FIG. 4 illustrates a one-half cross-sectional side view of heater 150including susceptor 155 and shaft 158. FIG. 4 shows shaft 158 having alongitudinally extending opening about its length to accommodate variouscomponents of heater 150. Those components include conductive leads 215a and 215 b to first heating element 250 and conductive leads 220 a and220 b to second heating element 260. Conductive leads 215 a, 215 b, 220a and 220 b are coupled at one end to one or more power supplies thatprovide the necessary energy to each heating element to supply therequisite temperature for the particular process.

As can be seen in FIG. 4, the conductive leads extend into the body ofsusceptor 155 of heater 150. Conductive leads 215 a and 215 b extendsuperiorly from shaft 158 into the body of susceptor 155 to a pointdefined approximately by a plane denoted by line A—A corresponding tothe location of first heating element 250 formed in the body ofsusceptor 155. Conductive leads 220 a and 220 b extend superiorly fromshaft 158 into the body of susceptor 155 to a point further from thesurface of susceptor 155 than conductive leads 215 a and 215 b.Conductive leads 220 a and 220 b extend to a point defined approximatelyby a plane denoted by line B—B corresponding to the location of secondheating element 260 formed in the body of susceptor 155.

FIG. 4 also shows a magnified view of the surface of susceptor 155. Inthis view, the surface of susceptor 155 is shown to have wafer packet156 that is an approximately 0.03 inch deep valley. A wafer loaded onthe surface of susceptor 155 sits within wafer pocket 156. Wafer packet156 serves, in one manner, to trap a wafer on the surface of susceptor155 or discourage a wafer from sliding off the surface of susceptor 155particularly during the wafer-load process. In one embodiment, waferpacket has an angled edge, for example, an edge having an angle, α of60° to 80°.

FIG. 4 also shows a magnified view of opening 198 to support lift pin195. In one embodiment, lift pin 195 has a head having a greaterdiameter than its body. Lift pin 195 rests flush with the surface ofsusceptor 155 (flush with the surface of wafer packet 156) when heater150 is in a “wafer-process” state. Accordingly, opening 198 has a wideenough diameter at its superior end to accommodate the head of lift pin195. Thus, for a lift pin having a head portion of a thickness ofapproximately 0.11 inches, the superior end of opening 198 will have adepth of 0.11 inches to accommodate the head of lift pin 195. Thediameter of opening 198 is narrowed below its superior end to preventlift pin 195 from escaping through the opening. It is to be appreciatedthat heat loss may be experienced through opening 198. Accordingly, inone embodiment, the diameter of opening 198 is minimized to reduce heatloss. For example, a diameter of the superior portion of opening 198 is0.180 inches to accommodate the head of a lift pin having a similar ofslightly smaller diameter. The remaining portion of opening 198 is 0.13inches to accommodate the body of a lift pin having a similar orslightly smaller diameter.

It is to be appreciated that, in certain instances, a CVD reactionprocess will be operated at other than atmospheric pressure. In the caseof LPCVD reaction conditions, for example, the pressure inside chamber145 (see FIG. 2, FIG. 3 and FIG. 4) is typically operated at, forexample, 1-250 torr. As noted, the exterior of heater 150 is exposed tothe reaction condition inside chamber 145. At the same time the exteriorsurfaces of heater 150 are exposed to this vacuum, the interior portionsof heater 150 are protected from the environment in chamber 145. Thus,for example, conductive leads 215 a, 215 b, 220 a and 220 b andthermocouple 210 are protected from the environment in chamber 145 bybeing placed in the opening or conduit through shaft 158 and into thebody of susceptor 155. In one embodiment, the pressure in the opening orconduit through shaft 158 is not subject to the vacuum that might bepresent in chamber 145. Instead, the opening or conduit through shaft158 is at atmospheric pressure. Therefore, the step motor that movesheater 150 (e.g., up and down) and lift plate 190 in chamber 145 issized to move against the vacuum force in the chamber. Thus, oneadvantage of the heater configuration of the invention is that thecomponents protected from the chamber environment in heater 150 may benested together so that the diameter of the shaft is not too large, andthe volume inside shaft 158 is not too great, to place unreasonabledemands on the motor that will move heater 150 (e.g., up and down)inside chamber 145. Placing the heating elements (e.g., first heatingelement 250 and second heating element 260) in separate planes of thebody of susceptor 155 allows such nesting. The nesting also minimizesheat loss in the system through the opening or conduit in shaft 158.

FIG. 5 shows a view of an embodiment of the heater of the inventionthrough the base of shaft 158. From this view, the individual conductiveleads 215 a and 215 b for first heating element 250 and 220 a and 220 bfor second heating element 260 are shown nested together in the centerof susceptor 155. Also shown nested with conductive leads 215 a, 215 b,220 a, and 220 b is thermocouple 210. As can be seen by thisillustration, the diameter of shaft 158 of heater 150 may be minimizedto, in this instance, approximately one third of the diameter ofsusceptor 155. FIG. 5 also shows four openings or throughbores 198 inthe body of susceptor 155. Openings or throughbores 198 support liftpins 195 that are used to, for example, raise and lower a wafer onto thesuperior surface of susceptor 155.

FIG. 6 shows a top cross-sectional view of susceptor 155 through lineA—A of FIG. 4. In this figure, first heating element 250 is shown formedin the plane defined by line A—A of FIG. 4. First heating element 250is, for example, comprised of two opposing coil portions 230 a and 230 bset forth in a mirror-image like fashion.

Coil portions 230 a and 230 b of first heating element 250 are formed inthe body of susceptor 155 in the plane defined by lines A—A of FIG. 4.Coil portions 230 a and 230 b of first heating element 250 are coupledto terminals 216 a and 216 b, respectively, to connect the coil portionsto a power source through conductive leads 215 a and 215 b,respectively. Coil portions 230 a and 230 b are, for example, of amaterial compatible with the current demand of the power source and thetemperature ranges for the heater. Coil portions 230 a and 230 b arealso selected, in one embodiment, to be of a material with thermalexpansion properties similar to aluminum nitride. As noted, a molybdenum(Mo) material having a thickness of approximately 2 mils formed in analuminum nitride (AlN) stage or susceptor is capable of generatingsusceptor temperatures (when coupled to an appropriate power supply) inexcess of 750° C. In one embodiment, opposing coil portions 230 a and230 b are separated at terminals 216 a and 216 b by approximately 3-5mm. The distance between the coil portions can be reduced to reduce anyeffective “cold zone” between the coil portions.

FIG. 7 shows a cross-sectional top view of susceptor 155 taken throughlines B—B of FIG. 4. FIG. 7 illustrates the plane of second heatingelement 260. In this embodiment, second heating element 260 is formed inthe body of susceptor 155 at a position further from the surface ofsusceptor 155 than first heating element 250 (i.e., the plane defined bylines A—A is nearer the surface of susceptor 155 than the plane definedby lines B—B). Similar to FIG. 6, second heating element 260 comprisesopposing coil portions 232a and 232b of, for example, molybdenum (Mo)formed in a mirror image fashion in the plane defined approximately bylines B—B. Coil portions 232 a and 232 b of first heating element 232are coupled to terminals 221 a and 221 b, respectively, to connect thecoil portions to a power source through conductive leads 220 a and 220b. In one embodiment, opposing coil portions 232 a and 232 b areseparated at terminals 221 a and 221 b by approximately 3-5 mm. Thedistance can be reduced to reduce any effective “cold zone” between thecoil portions.

In the embodiment illustrated in FIG. 6 and FIG. 7, coil portions 232 aand 232 b of second heating element 260 oppose one another in FIG. 7about axis 217 and coil portions 230 a and 230 b of first heatingelement 250 oppose one another in FIG. 7 about a similar axis. Acomparison of the figures shows that coil portions 232 a and 232 b arerotated 180° relative to coil portions 230 a and 230 b. In this manner,an area between opposing coil portions in either first heating element250 or second heating element 260 is compensated by the other heatingelement. It is to be appreciated that the configuration of heatingelement coils need not be offset by 180° as illustrated. Instead, theheating element coils may, for example, lie directly over one another(i.e., no compensation) or may overlap one another at a variety ofangles to compensate in some fashion the area between the opposing coilportions.

FIG. 8 shows a schematic top view of susceptor 155. The surface ofsusceptor 155 is divided into at least three zones. As shown in FIG. 8,area 245 forms a zone having an area defined by radius R₁. Area 245 isassociated with an area of susceptor 155 above shaft 158. Area 254 formsa zone having an area defined by radius R₂ minus area 245 defined byradius R₁. Area 255 is associated with the edge of susceptor 155 andforms a zone having an area defined by a radius R₃ minus area 254defined by radius R₂ and area 245 defined by radius R₁.

In one embodiment, first heating element 250 and second heating element260 have independent heat distribution and therefore may be controlledseparately. In this manner, first heating element 250 may receive moreor less power at certain points than certain points of second heatingelement 260. It is also to be appreciated at this point, that additionalheating elements may be added in the body of susceptor 155 to furtherdefine additional heating zones in the resistive heater. Considerationsfor incorporating multiple heating elements include locations in planesof susceptor 155 and nesting of additional conductive leads.

One way first heating element 250 and second heating element 260 areseparately controlled is by varying the width of each heating elementacross the area of the susceptor 155 while keeping the thickness of theheating element generally constant. It is generally recognized that, fora resistive heater, the power supplied to the heating element, and thusthe heat given off by the heating element, is directly related to theresistance in the heating element. For a resistive heating elementhaving a constant thickness, a wider portion of the heating element(i.e., greater volume) will have less resistance, will require lesspower to move a current, and will give off less heat than a narrowerportion of the heating element (i.e., smaller volume). Thus, by reducingthe width of a heating element at certain points (i.e., reducing thevolume of the heating element), the power supplied to the heatingelement will be greater at those points to move an amount of currentthrough the heating element than at points where the width of theheating element is not reduced. The temperature given off at the reducedpoints will similarly be greater than at points where the width of theheating element is not reduced. In turn, the power density, definedgenerally as the amount of power required to move an amount of currentthrough a length of a heating element, will be greater at those portionsof the heating element having a reduced width.

In FIG. 6, first heating element 250 is, for example, a molybdenum (Mo)material having a thickness of approximately 2 mils. The width of firstheating element 250 varies, in this example, to localize the powerdistribution to first heating element 250 in area 245 (see FIG. 8). Area245 is defined, in this example, to encompass an area above shaft 158.In one embodiment, where an opening is formed through shaft 158 toaccommodate thermocouple 210 and conductive leads 215 a, 215 b, 220 a,and 220 b, heat loss at an area of susceptor 155 will be greater over anarea of susceptor 155 associated with an area above shaft 158, denotedarea 245. Thus, the power density associated with area 245 in thatportion of heating element 250 will be greater than the power densityassociated with area 255 in that portion of heating element 250.

Referring to FIG. 6 and FIG. 8, in one example, a width, W₁, of firstheating element 250 in an area corresponding to area 245 (see FIG. 8) isless than a width, W₂, corresponding to area 255 (see FIG. 8) ofsusceptor 155 of heater 150. Current traveling through the smaller widthW₁ portion of first heating element 250 will encounter a greaterresistance than current traveling through other portions of heatingelement 250 (e.g., width W₂), and thus the heat given off by heatingelement 250 will be greater in area 245. For a molybdenum (Mo) materialheating element having a thickness of 2 mils, the width W₁, may be, forexample, 10 percent or less of the width W₂, to increase the powerdensity to area 245 relative to area 255. In one embodiment of amolybdenum material, the resistance throughout first heating element 250varies between a value of 2 ohms (e.g., width W₂) to a value of 4 ohms(e.g., width W₁).

Referring to FIG. 7 and FIG. 8, area 255 is defined, in this example toencompass an area corresponding to the edges of susceptor 155. In oneembodiment, heat loss of an area of the surface of susceptor 155 will begreater at its edges, denoted area 255. Thus, for example, the powerdensity associated with area 255 in that portion of heating element 260will be greater than the power density associated with other areas ofsusceptor 155.

Referring to FIG. 7 and FIG. 8, second heating element 260 is, forexample, a molybdenum (Mo) material having a thickness of approximately2 mils. The width of second heating element 260 varies, in this example,to localize the power density to second heating element 260 in area 255(see FIG. 8). Thus, a width, W₄, of second heating element 260 in anarea corresponding to area 255 (see FIG. 8) is less than a width, W₃,corresponding to other areas of susceptor 155 of heater 150. Currenttraveling through the smaller width W₄ portion of heating element 260will encounter a greater resistance than current traveling through otherportions of heating element 260 (e.g., width W₃), and thus the heatgiven off by heating element 260 will be greater in area 255. For amolybdenum (Mo) material heating element having a thickness of 2 mils,the width, W₄, may be, for example, 10 percent or less of the width, W₃,to increase the power distribution to area 255 relative to area 245. Inone embodiment of a molybdenum material, the resistance throughout firstheating element 250 varies between a value of 2 ohms (e.g., W₃) and 4ohms (e.g., W₄).

FIG. 9 graphically illustrates the individual control of the heatingelements for the surface of susceptor 155 of heater 150. FIG. 9 showsthe power ratio supplied to the first heating element and the secondheating element versus the radius of the susceptor 155. The power ratiois defined in this embodiment as the ratio of power of first heatingelement 250 and the power of second heating element 260. As indicated,the power ratio of first heating element 250 is greater in area or zone245 than other zones of susceptor 155 due to the additional powersupplied to first heating element 250. Similarly, the power ratio isgreater in area or zone 255 due to the additional power supplied tosecond heating element 260 in that area or zone than other areas ofsusceptor 155.

A multi-zone resistive heating element such as illustrated in FIGS. 4-8allows individual areas or zones of a susceptor of a heater to beseparately addressed, thereby providing more temperature uniformityacross the surface of the susceptor than single-zone resistive heaters.For example, a dual-zone resistive heater such as shown in FIGS. 4-8allows a first zone (area 245) to be addressed individually of otherareas of susceptor 155. Thus, heat loss through shaft 158 may beaccommodated without sacrificing temperature uniformity across thesurface of susceptor 155. Similarly, a second zone (area 255) may beaddressed individually of other areas of susceptor 155. Thus, heat lossat the edges of susceptor 155 (even at temperatures of 750° C. or more)may be accommodated without sacrificing temperature uniformity acrossthe surface of susceptor 155. Thus, for high temperature applications(e.g., approximately 750° C. or more), the separate areas may becontrolled so that heat loss, for example, at an area associated withshaft 158 and the edges of susceptor 155 may be compensated by increasedpower distribution to first area 245 and second area 255. Thetemperature across the surface of susceptor 155 may therefore bemaintained at a more constant value than prior art single zone resistiveheaters.

In FIGS. 4-8, first heating element 250 and second heating element 260occupy approximately the same area of susceptor 155. One advantage ofsuch a configuration is that, in the event that one heating elementfails, the other heating element may be configured to heat the entiresurface of susceptor 155. It is to be appreciated that the individualheating elements need not occupy similar areas of susceptor 155, but maybe configured to occupy only specific areas such as area 245 or area255.

In FIGS. 4-8, first heating element 250 is located in the plane(represented by lines A—A of FIG. 4) closer to the superior surface ofsusceptor 155 than the plane of second heating element 260 (representedby lines B—B of FIG. 5). In one embodiment, first heating element 250 isapproximately 5-8 mm from the surface of susceptor 155. Separating firstheating element 250 from the surface in this manner provides bettertemperature distribution and decreases localized heating.

It is to be appreciated that the placement of the respective heatingelements will vary according to the process conditions and the processobjectives. One reason for placing second heating element 260 in a planeof the body of susceptor 155 lower than a plane associated with firstheating element 250 is that the power supplied to second heating element260 may be greater than that supplied to first heating element 250. Sucha situation will occur when, for example, the heat loss at the edges ofthe surface of susceptor 155 is greater than the heat loss at the centerof surface of susceptor 155. Accordingly, the additional power (e.g.,higher power density) supplied to the edges of susceptor 155 as comparedto the center of susceptor 155 can, in one instance, be distributedbetter as a result of the greater difference between the location ofsecond heating element 260 (denoted by lines B—B) and the surface ofsusceptor 155 than if that heating element was located in a plane closerto the surface of susceptor 155. The better distribution reduces thepotential for localized heating or “hot spots” providing a more uniformdistribution of the heat at the surface of susceptor 155. Bydistributing the heat more uniformly through the location of secondheating element 260, the ability to control the temperature of thesurface of susceptor 155 to, for example, ±3° C. even at temperatures of750° C. or greater at any particular spot is facilitated. The more evendistribution also reduces the likelihood of susceptor cracking ordamage.

FIGS. 10 and 11 illustrate one embodiment for monitoring or indicatingthe temperature of the surface of susceptor 155. FIG. 10 schematicallyshows a portion of the top surface of the chamber body, specifically, aportion of chamber lid 170 and a portion of perforated face plate 180.Extending through openings in chamber lid 170 are two pyrometers, firstpyrometer 200 and second pyrometer 205. FIG. 11 shows a top view ofchamber lid 170 having first pyrometer 200 and second pyrometer 205coupled thereto. First pyrometer 200 and second pyrometer 205 are, forexample, available from Sekidenko, Inc. of Vancouver, Wash. Eachpyrometer provides data about the temperature at the surface ofsusceptor 155 (or at the surface of a wafer on susceptor 155). In oneembodiment, each pyrometer has a temperature measurement range of 335°C. to 1200° C. Each pyrometer measures the temperature of susceptor 155in an area corresponding to the location of the pyrometer. In theexample shown in FIG. 11, first pyrometer 200 measures a temperature ofsusceptor 155 in area or zone 245 while second pyrometer 205 measures atemperature of susceptor 155 in area or zone 254. Thermocouple 210measures the temperature at a surface of susceptor 155 correspondingapproximately or near to center 235 of susceptor 155. It is to beappreciated that the pyrometers and thermocouple are exemplary and otherdevices may be used as temperature indicators. For example, thermalcameras may be substituted for the pyrometers in another embodiment ofthe invention.

Since first pyrometer 200 and second pyrometer 205 provide a temperaturemeasurement based in part on the radiant energy or light to which thepyrometer is exposed, each pyrometer must have access to the inside ofchamber 145. Access, in this case, is provided by windows 290 and 295 atthe base of first pyrometer 200 and second pyrometer 205, respectively,and openings 270 and 275 formed in chamber lid 170, respectively, andopenings 280 and 285, respectively, formed in face plate 180. In certainembodiments, such as a CVD deposition process, there may be a concernabout the possible coating of windows 290 and 295, that might disruptthe available radiation or light to first pyrometer 200 and secondpyrometer 205, respectively, causing the temperature measurement of thepyrometers to fail. Accordingly, in one embodiment, the length andwidth, particularly of openings 280 and 285 but also possibly ofopenings 270 and 275 are configured to minimize the possibility ofcoating windows 290 and 295. In one embodiment, the ratio of theopenings is related to the thickness of faceplate 180. A suitablerelation for openings to faceplate thickness is 1 to 3.

In one embodiment, the multiple temperature measurements are used toregulate and control the temperature of the surface of susceptor 155.For example, in an LPCVD process for the deposition of Si₃N₄, a surfacereaction temperature of 750° C. may be desired with a ±2.5° C.temperature difference across the surface of susceptor 155 of heater150. The system of the invention may regulate and control thetemperature of heater 150 by measuring a temperature at midpoint 235 ofsusceptor 155 (measured, in this embodiment, by thermocouple 210) whichis used as a reference temperature or control temperature. Thetemperature uniformity across susceptor 155 is measured by thetemperature difference of first pyrometer 200 and second pyrometer 205,ΔT. From the measured ΔT, the system will adjust the power ratio of thefirst heating element and the second heating elements to control the ΔTin a certain range, such as ±2.5° C. at 750° C. for a Si₃ N₄ LPCVDprocess. The advantages of using a temperature difference (e.g., ΔT)measurement are at least two fold. First, emissivity changes betweenwafers will effect the absolute measurement of each pyrometer, but willnot effect the relative value of ΔT. Second, changes in the condition ofthe chamber over time will not effect the relative temperaturemeasurement but generally will effect the absolute temperaturemeasurement.

FIG. 12 describes a general method of processing a wafer in a reactorconfigured according to an embodiment of the invention. FIG. 12describes a method of controlling the temperature in a dual-zone,single-wafer, resistive heater during, for example, a CVD process. As afirst step (step 300), heater 150 in chamber 145 of a CVD reactor isplaced in a wafer-load position (see FIG. 3 and the accompanying text).Next, a wafer is loaded onto susceptor 155 using, for example, a robotictransfer mechanism (step 310). Heater 150 is then positioned so that thewafer is adjacent perforated face plate 180 (step 320) as illustrated,for example, in FIG. 1. The reactor is then ramped to processtemperature (step 330). In an LPCVD process for the deposition of Si₃N₄,for example, the temperature is ramped to 750° C. The temperature ismeasured at thermocouple 210 and one or both of first pyrometer 200 andsecond pyrometer 210 to coordinate the temperature across the surface ofsusceptor 155 of heater 150 (step 340). The temperature is controlled byregulating the power supply to first heating element 250 and secondheating element 260 (step 350).

Once the reaction is complete and the desired film thickness isachieved, the process gas supplied to the chamber is discontinued andthe chamber is purged with an inert gas such as nitrogen (step 370).Next, the heater stage is moved to the wafer-load position (see FIG. 3and the accompanying text) and the processed wafer is removed andreplaced by another wafer (step 380).

The above description related to controlling the temperature of thesurface of susceptor 155 of heater 150 and thus the surface reactiontemperature of a wafer on the surface of susceptor 155 by controllingand regulating the temperature in different areas or zones of susceptor155. It is to be appreciated that this control and regulation may bedone manually or with the aid of a system controller. In the formerinstance, an operator may record temperature measurements of thedifferent temperature indicators (e.g., first pyrometer 200, secondpyrometer 205, and thermocouple 210) and manually adjust the powersupplied to either or both first heating element 250 and second heatingelement 260. Alternatively, a controller may be configured to record thetemperature measured by the temperature indicators and control the powersupplied to the heating elements based, for example, on an algorithmthat determines a relative value of the temperature difference andadjusts the heating elements accordingly.

FIG. 13 schematically illustrates a system for controlling first heatingelement 250 and second heating element 260 based on temperaturemeasurements provided by indicators such as, for example, firstpyrometer 200, second pyrometer 205, and thermocouple 210, provided tocontroller 225. In one embodiment, controller 225 contains a suitablealgorithm to compare the temperature difference of at least two of thetemperature indicators and control power supply 215 to coordinate thetemperature of heater 150 so that the temperature indicators are withinacceptable ranges. For example, in the example where the temperature ofheater is desired to be 750° C.±2.5° C. across the surface of susceptor155 of heater 150, controller 225 controls power supply 215 to achievethis result based on measurements provided by at least two indicators.

Controller 225 is supplied with software instruction logic that is acomputer program stored in a computer readable medium such as memory incontroller 225. The memory is, for example, a portion of a hard diskdrive. Controller 225 may also be coupled to a user interface thatallows an operator to enter the reaction parameters, such as the desiredreaction temperature and the acceptable tolerance of a temperaturedifference between indicators (e.g., ±3° C.). In an LPCVD reactionprocess, controller 225 may further be coupled to a pressure indicatorthat measures the pressure in chamber 145 as well as a vacuum source toadjust the pressure in chamber 145.

Generally, heater element control takes place by either voltage orcurrent regulation. The power output of the heater element is equivalentto, by voltage

Power=voltage²/resistivity.

In FIG. 13, controller 225 is supplied with a desired operatingtemperature (provided by temperature set point 201). Controller 225controls power supply 215 which supplies the necessary voltage to firstheating element driver 216 and second heating element driver 217. Theheating element drivers in turn control the voltage applied to firstheating element 250 and second heating element 260, respectively.Controller 225 controls the ramp rate of heater 150 and the voltage orpower ratio of heater 150 (ramp rate/PID control 203 and voltage ratio202, respectively).

The following describes an embodiment of multiple zone heater controlusing, for example, the system described in FIG. 13. Multiple zoneheater temperature is controlled with one temperature sensor at an innerzone (e.g., area or zone 245), while a calibrated correlation functionis set between the inner zone (e.g., area or zone 245) and outer zone(e.g., area or zone 254 or area or zone 255). The temperature controladopts two methodologies. When the heater temperature is close to theset point and is within proportional plus integral derivative forward(PIDF) servo band, the PIDF control algorithm is used to regulate theheater temperature to the set point. On the other hand, when the heateris in ramping up or cooling down mode, and its temperature is out of thePIDF servo band, the ramp algorithms are used to control the heatertemperature with a predefined rate of heating or cooling to prolongheater life. The dual zone heater temperature uniformity is controlledby voltage ratio or power ratio between the inner and outer zones. Theratio is not a constant, but needs to be changed as the temperaturechanges because the heat loss increases differently between inner andouter zones of the susceptor as heater temperature increases. The ratiosetting is also dependent on the chamber condition, such as chamberpressure and gas flow.

The heater control modes can be divided into ramp control and PIDFcontrol. The ramp control can be further divided as “low temperatureramp” and “high temperature ramp” by temperature range with differentvoltage or power ratios. The “low temperature ramp” adopts a fixedvoltage ratio. The “high temperature ramp” adopts a varied voltage orpower ratio that is calculated through formula.

I. Control Condition

The chamber operation condition can be divided into two modes: “chamberOFF line/ON line” and “recipe” operation. The operating sequences may beas follows:

A. Chamber OFF line/ON line:

When the heater starts to heat up, to set the temperature, the controlsteps are:

1. Low temperature ramp, when the heater temperature is under thepredefined temperature.

2. High temperature ramp, when the heater temperature is over thepredefined temperature.

3. PIDF servo, when the heater temperature reaches the requestedtemperature within the predefined servo band.

When the heater starts to cool down, the control steps are reversed:

A. High temperature ramp, when the heater temperature is over apredefined temperature.

B. Low temperature ramp, when the heater temperature is under apredefined temperature.

C. PIDF servo, when the heater temperature reaches the requestedtemperature within the predefined servo band.

The ramp rate and other PID factors follow predefined system constants.

B. Recipe Operation:

In recipe operation, the heater control contains the temperature controlrequirement parameters: temperature setting, voltage ratio, and ramprate (if the temperature required is different from previous step).

For a clean recipe, the control sequence is for example:

33. PIDF servo at process temperature.

34. Ramp down to clean temperature.

35. PIDF servo at clean temperature.

36. Ramp up to process temperature.

37. PIDF servo at process temperature.

During the PIDF servo, the voltage ratio is listed in step of recipe.During the ramp up or down, the ramp rate is listed in step of recipeand the voltage ratio follows the predefined value as used in “chamberOFF line/ON line.”

II. Ramp Control

One algorithm used for ramp control is described in the below equationswhich use proportional control on the ramp rate of the heatertemperature.

Heater Ramp Voltage:

Inner Zone Heater Ramp Voltage=Previous Inner Zone Heater Ramp Voltage+([Ramp P Gain]*(Target Ramp Rate−Actual Ramp Rate))

Outer Zone Heater Ramp Voltage=Voltage Ratio*Inner Zone Heater RampVoltage

When Outer Zone Heater Ramp Voltage>100% (e.g., 10V), let

Outer Zone Heater Ramp Voltage=100% (e.g., 10V) and

Inner Zone Heater Ramp Voltage=Outer Zone Heater Ramp Voltage/VoltageRatio

Target Ramp Rate is heater temperature ramp rate in Online/Offline, andTarget Ramp Rate can be overwritten by “Ramp Rate” in “Clean” recipe.Table 1 presents a description of each parameter in the above equationsand provides a representative recommended value for an LPCVD chamber.

TABLE 1 Heater Parameter Description-Ramp Control Inner Zone HeaterPower Output Ramp Rate (Limitation of Change of Ramp Rate) Description:Maximum rate at which analog output from system controller can change.Recommended Value: 100 mV Temperature Error to Switch to PID ControlDescription: Temperature band at which to switch from ramp control toPID control and vice versa. Recommended Value: 10° C. Temperature RampProportional Gain (Ramp P Gain) Description: Proportional Gain used tocalculate heater voltage during ramp control. Recommended Value: 8Chamber X Heater Temperature Ramp Rate Heater Temperature Ramp Rate(Target Ramp Rate) Description: Rate at which temperature should rise orfall. Recommended Value: 0.15° C./Sec Voltage Ratio Parameter:Description: Voltage ratio between outer zone and inner zone at controltemperature. This parameter varies for different temperatures. See“Voltage Ratio” section for detail. Thermocouple Failure DetectionTime-out Description: Time to signal an alarm if the actual ramp rate isless than 70% of the target ramp rate. Recommended Value: 300 seconds

For Ramp Control, the voltage ratio depends on the heater temperaturerange.

A. If Current temperature (° C.)<[T_(L)]:

then Voltage Ratio=[R_(L)]

Note: R_(L)=Voltage Ratio of Low Temperature Ramp

T_(L)=Temperature Limit of Low Ramp (° C.)

B. If [T_(L)]<Current Temperature (° C.)<Setting Temperature (°C.)−[Temperature Error to Switch PID Control] then VoltageRatio=[R_(L)]+([R_(H)]−[R_(L)])*(Currenttemperature−[T_(L)])/([T_(H)]−[T_(L)])

Note: R_(L)=Voltage Ratio of Low Temperature Ramp

R_(H)=Voltage Ratio of High Temperature Ramp

T_(H)=Temperature Limit of High Ramp (° C.)

T_(L)=Temperature Limit of Low Ramp (° C.)

R_(L), R_(H) are limited by Maximum Voltage Ratio of Two Zones (R_(M))

C. In Recipe (process and clean):

The Voltage Ratio depends on the desired heater temperature range.

At Process Temperature:

Voltage Ratio=Voltage Ratio at Process Temperature in the recipe.

When heater temperature ramp down or up before each Request Temperature(° C.) in recipe−[Temperature Error to Switch PID Control].

Voltage Ratio=[R_(L)]+([R_(H)]−[R_(L)])*(Currenttemperature−[T_(L)])/([T_(H)]−[T_(L)])

Note: R_(L)=Voltage Ratio of Low Temperature Ramp

R_(H)=Voltage Ratio of High Temperature Ramp

T_(H)=Temperature Limit of High Ramp (° C.)

T_(L)=Temperature Limit of Low Ramp (° C.)

R_(L), R_(H) are limited by Maximum Voltage Ratio of Two Zones (R_(M))

Recalculated Voltage Ratio by every 10° C. temperature change.

III. PIDF Control

PIDF control is used when the heater temperature is within thetemperature band set by the system. Within the PIDF control band, up tofive different parameters are used to calculate the total heatervoltage. These five parameters are feedforward, temp preset, P, I, andD. The feedforward leg provides the voltage necessary to sustain thetemperature at a certain setpoint. When there is no load, it should bethe only component contributing to the total heater voltage. One purposeof adding feedforward is to provide control stability for differentheaters whose resistance may vary. The temp preset is available inprocess recipes to provide an instantaneous voltage change to the heaterwhen large loads may be present on the heater during gas introduction orpressure ramp. The P leg is determined by multiplying the temperatureerror by a gain, the I leg is determined by multiplying the totaltemperature error by a gain, and the D leg is determined by multiplyingthe temperature error slope by a gain. The I leg is used only nearsteady state conditions when the temperature is near the setpoint. The Ileg is not used in the total voltage calculation when temp preset isused during process.

Inner zone heater voltage during PIDF control is determined according tothe equations in Table 2. The D leg is subtracted from the total voltagewhile the other legs are added. The equations for the individual legsare shown with some example calculations. The I leg and Temp Preset legare exclusive of each other. The I leg contributes to the total voltageonly when Temp Preset is zero. If the Temp Preset is not zero, the I legis not used.

Outer zone heater voltage during PIDF control is determined by theproduct of the inner zone PID control output voltage and the voltageratio (power correlation). The voltage ratio (power correlation) mightbe a table or listing calibrated based on real process conditions,heaters from different manufacturers, as well as hot idle conditions.

TABLE 2 PID Control Equations Inner Zone Heater PID Voltage =(Feedforward leg + P leg + I leg + Temp Preset leg) − D leg Outer ZoneHeater Voltage = Voltage Ratio*Inner Zone Heater Control Voltage WhenOuter zone Heater Voltage > 100% (10 V), let Outer zone Heater Voltage =100% (10 V) Inner Zone Heater Voltage = Outer zone Heater Ramp Voltage/Voltage Ratio Feedforward leg = Temperature setpoint*([Bias wattage perdegree])/({Maximum Watts of Inner] + [Maximum Watts of Outer]*VoltageRatio{circumflex over ( )}2)) P leg = Temperature error*([PGain]*[Correction Power per Degree of error]/([Maximum Watts of Inner] +[Maximum Watts of Outer]*Voltage Ratio{circumflex over ( )}2)) I leg =Temperature error total*([I Gain]*[Correction Power per Degree oferror]/([Maximum Watts of Inner] + [Maximum Watts of Outer]*VoltageRatio{circumflex over ( )}2)) D leg = Temperature error slope*([DGain]*[Correction Power per Degree of error]/([Maximum Watts of Inner] +[Maximum Watts of Outer]*Voltage Ratio{circumflex over ( )}2)) TempPreset leg = [Temp Preset]/([Maximum Watts of Inner] + [Maximum Watts ofouter]*Voltage Ratio{circumflex over ( )}2))

EXAMPLE

(Inner) Heater PID Voltage=(49.1%+3.4%+3.0%+0%)−2.0%=53.5%=>107VAC

Feedforward leg=750*(0.655/(2000+2000*2{circumflex over ( )}2)=>49.1%* Pleg=0.8*(142.7*30/(2000+2000*2{circumflex over ( )}2)=>3.4%

(Outer) Heater Voltage=1.15*107=>123VAC Power Ratio=1.5

*Note: Arrows in calculations indicate that the calculated value shownis different in magnitude by a factor of 10^(×).

TABLE 3 Heater Parameter Description-PID Control Chamber X watts ofpower at maximum Inner analog output (maximum Watts of Inner)Description: Used as a gain factor in calculations for Feedforward leg,P leg, I leg, D leg, and Temp Preset leg. Chamber X watts of power atmaximum Outer analog output (Maximum Watts of Outer) Description: Usedas a gain factor in calculations for Feedforward leg, P leg, I leg, Dleg, and Temp Preset leg. Chamber X resistive heater servo band widthDescription: Temperature band around setpoint within which integralcontrol is used. Integral control is reset every time temperature isoutside this band. Recommended Value: 15° C. Chamber X correction powerper degree of error (Correction Power per degree of error) Description:Gain factor used in P, I, and D legs. Recommended Value: 30.0 W/° C.Chamber X outer zone voltage servo ratio (Voltage Ratio) Description:Voltage ratio is used for outer zone voltage servo calibration factorbased upon the inner zone PID servo value. It relates to electrical loadchange, i.e., current. Chamber X servo by percent of error history total(I gain) Description: Gain factor for I leg. I leg is used to correctsteady state error and is used only when heater temperature is close tosetpoint. I leg is used only when there is no temp preset in the recipe.Chamber X servo by percent of present error (P Gain) Description: Gainfactor for P leg. P leg is used to counter any load disturbance caused bgas flow, cool wafer, etc. Chamber X servo by percent of present slope(D Gain) Description: Gain factor for D leg. D leg is used to reduceoscillations in the temperature. It is subtracted from the total powerand acts to oppose sudden changes in temperature. Chamber X heater biaswattage per degree setpoint (Bias wattage per degree) Description: Gainfactor for Feedforward leg. Feedforward leg should be tuned such that itcontributes all the voltage to the total heater voltage when at hot idle(no load) Recommended Value: 0.25 W/° C. (varies from heater to heaterwhen tuned) Temp Preset (Temp Preset) Programmed in Recipe Description:Provides an instantaneous change in voltage when requested in recipe.Used during gas flow introduction when a large load is present on theheater. When temp preset is used, I leg becomes zero. Temp preset shouldbe zero for I leg to be used, especially during deposition steps.Recommended Value: Depends on recipe. Every 50 mW of Temp Preset adds1.8% voltage to the heater for a multiple zone heater.

For PIDF control, the voltage ratio depends on the heater temperaturerange.

A. If Setting temperature (° C.) is below [TL]:

Voltage Ratio=[R_(L)]

Note: R_(L)=Voltage Ratio of Low Temperature Ramp

T_(L)=Temperature Limit of Low Ramp (° C.)

B. If Setting Temperature (° C.) is between [T_(L)] and [T_(H)]

Voltage Ratio=[R_(L)]+([R_(H)]−[R_(L)])*(Settingtemperature−[T_(L)])/([T_(H)]−[T_(L)])

Note: R_(L)=Voltage Ratio of Low Temperature Ramp

R_(H)=Voltage Ratio of High Temperature Ramp

T_(H)=Temperature Limit of High Ramp (° C.)

T_(L)=Temperature Limit of Low Ramp (° C.)

C. Voltage Ratio—In Recipe (process/clean):

Within Process Temperature+Temperature Error to Switch PID Control

Voltage Ratio=Voltage Ratio at Process Temperature in recipe. Voltageratio setting is limited by Maximum Voltage Ratio of Two Zones (R_(M)).

Table 4 describes the heater parameters for heat up, standby/process,and cooling down.

TABLE 4 Heater Parameter Description-Heat up, standby/process, coolingdown Heater Parameter Description - (syscons are located in HeaterCalibration Screen under Process/Chamber Parameters) Chamber XTemperature Limit of Low Ramp (° C.) (T_(L)) Description: When theheater is over this temperature, the voltage ratio of two zones is equalto Basic Voltage Ratio. Recommended Value: 750° C. (settable: 600° C. to800° C.) Standby Temperature (° C.) Description: When the chamber isunder standby condition, the heater is maintained at this temperature.Recommended Value: Process temperature + 10° C. Chamber X Voltage Ratioof Low Temperature Ramp (R_(L)) Description: Voltage ratio between outerzone and inner zone under the temperature of [Temperature Limit of LowRamp (° C.) (T_(L))] Chamber X Voltage Ratio of High Temperature Ramp(R_(H)) Description: Voltage ratio between outer zone and inner zoneequal over the temperature of [Temperature Limit of High Ramp (° C.)(T_(H))] Maximum Voltage Ratio of Two Zones (R_(M)) Description: Themaximum voltage ratio. Includes R_(H), R_(L) and R in the recipe.Allowed Range 0 to 2.2 Value: Temperature Setting (° C.) (Ts)Description: Heater target operating temperature. When the heater is atthis temperature, the Voltage Ratio of the two zones is equal to BasicVoltage Ratio. Voltage Ratio of Setting Temperature Description: Whenthe temperature reaches the setting temperature within [Chamber Xresistive heater servo bandwidth (° C.)], the controller is using thisvoltage ratio to do PIDF control.

Table 5 describes the heater parameters for a chamber clean recipe.

TABLE 5 Heater Parameter Description - Clean Recipe Heater ParameterDescription - (parameter are located in Recipe) Process Temperature (°C.) Parameter: Programmed in Recipe Description: When the chamber is atprocess condition, the heater is served to this temperature. RecommendedValue: Depends on process Voltage Ratio at Process Temperature Syscon:Programmed in Recipe Description: Voltage ratio between outer zone andinner zone at process temperature within the [Servo band] LimitationValue: R_(M) Ramp Rate (up or down) (° C./Minute) (over write the TargetRamp Rate) Parameter: Programed in Recipe Description: The temperaturesetting is different from previous step. The Ramp rate of heatertemperature is needed to be set and be controlled by software.Limitation Value: . . .° C./Minute

The above description relates primarily to the use of a multi-zone,single-wafer heater for use in a CVD system. The invention has beendescribed including a dual-zone heater apparatus. It is to beappreciated that additional heating elements and temperature indicatorsassociated with the heating elements may be included without departingfrom the spirit or scope of the invention. It is also to be appreciatedthat the invention is not to be limited to CVD reactors, systems, ormethods, but may find use in a variety of other applications whereaccurate temperature control is warranted.

In the preceding detailed description, the invention is described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention as setforth in the claims. The specification and drawings are, accordingly, tobe regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. An apparatus comprising: a stage comprising asurface having an area to support a wafer and a body; a shaft coupled tothe stage; a first heating element disposed within a first plane of thebody of the stage; and a second heating element disposed within a secondplane of the body of the stage that is a greater distance from thesurface of the stage than the first plane of the body, wherein the firstheating element supplies a variable heat energy to an area of thesurface of the stage.
 2. The apparatus of claim 1, wherein the firstheating element occupies an area of the stage substantially the samesize as an area of the stage occupied by the second heating element. 3.The apparatus of claim 1, wherein the stage comprises a first surface tosupport a wafer and a second surface, and the shaft has a portiondefining an interior opening through a length of the shaft, wherein theshaft is coupled to the second surface of the stage at a pointsubstantially corresponding to the midpoint, and power leads to each ofthe first heating element and the second heating element are disposed inthe opening.
 4. The apparatus of claim 1, wherein the stage body issubstantially cylindrical such that a midpoint corresponds to an axisnormal to the surface and a first portion of the area of the stage isdefined by a first radius about the axis and a second portion of thearea is defined by a second radius about the axis greater than the firstradius.
 5. The apparatus of claim 4, wherein the first heating elementis a resistive heating element comprising a first resistance in an areacorresponding with the first portion of the area of the stage and asecond resistance in an area corresponding with the second portion ofthe area of the stage, and wherein the second heating element is aresistive heating element comprising a first resistance in an areacorresponding with the first portion of the area of the stage and asecond resistance in an area corresponding with the second portion ofthe area of the stage.
 6. The apparatus of claim 5, wherein the firstresistance of the first heating element is less than the secondresistance of the first heating element and the first resistance of thesecond heating element is greater than the second resistance of thesecond heating element.
 7. The apparatus of claim 4, wherein the powerdensity of the first heating element is greater than the power densityof the second heating element in an area corresponding with the firstportion of the area of the stage and the power density of the secondheating element in an area corresponding with the second portion of thearea of the stage.
 8. The apparatus of claim 1, wherein the firstheating element is disposed about the first portion in a pair of coilsand the first portion is defined by two segments separated by a firstaxis, a first coil disposed in a first segment of the first portion anda second coil disposed in a second segment of the first portion, thefirst coil coupled to the second coil through the first axis, whereinthe second heating element is disposed about the second portion in apair of coils and the second portion is defined by two segmentsseparated by a second axis, a first coil disposed in a first segment ofthe second portion and a second coil disposed in a second segment of thesecond portion, the first coil coupled to the second coil through thesecond axis, and an intersection of the first axis and the second axisdefines an angle in a plane of the surface between 0° and 180°.
 9. Theapparatus of claim 8, wherein the stage body is substantiallycylindrical such that a midpoint corresponds to an axis normal to thesurface and a first portion of the area of the stage is defined by afirst radius about the axis and a second portion of the area is definedby a second radius about the axis greater than the first radius, whereinthe power density of the first heating element is greater than the powerdensity of the second heating element in an area corresponding with thefirst portion of the area of the stage and the power density of thesecond heating element in an area corresponding with the second portionof the area of the stage.
 10. The apparatus of claim 1, wherein thestage is comprised of a material that is resilient to temperatures inexcess of 750° C.
 11. The apparatus of claim 10, wherein the stage andthe shaft are comprised of aluminum nitride.
 12. The apparatus of claim11, wherein the stage is comprised of aluminum nitride and has a thermalconductivity in the range of 140 W/mK to 200 W/mK and the shaft iscomprised of aluminum nitride and has a thermal conductivity in therange of 60 W/mK to 100 W/mK.
 13. The apparatus of claim 1, wherein thearea to support a wafer includes a wafer pocket depressed in the surfaceof the stage and having sidewalls disposed at an angle of approximately60° to 80° relative to a plane perpendicular to the surface of thestage.
 14. An apparatus comprising: a stage comprising a surface havingan area to support a wafer and a body; a shaft coupled to the stage; afirst heating element disposed within a first plane of the body of thestage; and a second heating element disposed within a second plane ofthe body of the stage that is a greater distance from the surface of thestage than the first plane of the body, wherein the first heatingelement is a resistive heating element comprising a first portion havinga first resistance and a second portion having a second resistancedifferent than the first resistance.
 15. The apparatus of claim 14,wherein the second portion of the first heating element is disposedwithin an area of the stage at a greater distance from a midpoint of thearea than the first portion of the first heating element.
 16. Theapparatus of claim 14, wherein the second heating element is a resistiveheating element comprising a first portion having a first resistance anda second portion having a second resistance different than the firstresistance.
 17. The apparatus of claim 16, wherein the second portion ofthe second heating element is disposed within an area of the stage at agreater distance from a midpoint of the area than the first portion ofthe second heating element.
 18. A reactor comprising: a chamber; and aresistive heater comprising a stage disposed within the chamberincluding a surface having an area to support a wafer and a body, ashaft coupled to the stage, a first heating element disposed within afirst portion of the area of the stage and within a first plane of thebody of the stage, and a second heating element disposed within a secondportion of the area of the stage and in a second plane of the body ofthe stage, the second plane of the body of the heater is a greaterdistance from the surface of the stage than the first plane of the body,wherein a power density of the first heating element is greater than apower density of the second heating element in an area correspondingwith a first portion of the stage area and the power density of thefirst heating element is less than the power density of the secondheating element in an area corresponding with a second portion of thestage area.
 19. The reactor of claim 18, wherein the stage body issubstantially cylindrical such that a midpoint corresponds to an axisnormal to the surface and the second stage area is disposed at a greaterdistance from the midpoint than the first stage area.
 20. The reactor ofclaim 18, wherein the first heating element is disposed about the firstportion in a pair of coils and the first portion is defined by twosegments separated by a first axis, a first coil disposed in a firstsegment of the first portion and a second coil disposed in a secondsegment of the first portion, the first coil coupled to the second coilthrough the first axis, wherein the second heating element is disposedabout the second portion in a pair of coils and the second portion isdefined by two segments separated by a second axis, a first coildisposed in a first segment of the second portion and a second coildisposed in a second segment of the second portion, the first coilcoupled to the second coil through the second axis, and an intersectionof the first axis and the second axis defines an angle in a plane of thesurface between 0° and 180°.
 21. The reactor of claim 18, furthercomprising: a first temperature sensor disposed within the shaftpositioned to measure a first temperature of the stage; and a secondtemperature sensor positioned to measure a second temperature in an areaof the stage corresponding to one of the first portion of the area ofthe stage and a second portion of the area of the stage.
 22. The reactorof claim 21, wherein the first temperature sensor is a thermocouple. 23.The reactor of claim 21, wherein the second temperature sensor is apyrometer.
 24. The reactor of claim 23, wherein the chamber comprises atop surface and the pyrometer is disposed in a window in the top surfaceof chamber.
 25. The reactor of claim 18, wherein the shaft has a portiondefining an interior opening through a length of the shaft, the reactorfurther comprising a power source coupled to the first heating elementand the second heating element through the opening in the shaft.
 26. Thereactor of claim 25, further comprising a controller coupled to thepower source to control the temperature of the first heating element andthe second heating element.
 27. The reactor of claim 26, wherein thecontroller controls the temperature of the first heating element and thesecond heating element to within ±3° C.
 28. The reactor of claim 27,wherein the controller is coupled to at least two of the firsttemperature sensor, and the second temperature sensor.
 29. The reactorof claim 18, wherein the heater is comprised of a material that isresilient to temperatures in excess of 750° C.
 30. The reactor of claim29, wherein the stage is comprised of aluminum nitride and has a thermalconductivity in the range of 140 W/mK to 200 W/mK.
 31. The reactor ofclaim 18, wherein the body of the heater has a bottom surface and aportion defining an opening through the body and substantially normal tothe surface, the reactor further comprising: a lift pin having a firstend and a second end, the first end disposed within the opening throughthe body of the heater and the second end extending below the bottomsurface of the body of the heater, a lifter assembly coupled to theshaft to move the heater between a first position and a second positionwithin reactor chamber; and a lift plate coupled to the lifter assemblyand having a portion disposed in the chamber, the portion disposed inthe chamber including a surface extending in a direction normal to theshaft and substantially parallel to the top surface of the body of thestage, so that, when the heater is in the first position, the lift pincontacts the lift plate.
 32. The reactor of claim 31, wherein the liftplate is comprised of a material that is resilient to temperatures inexcess of 750° C.
 33. The reactor of claim 32, wherein the lift plate iscomprised of aluminum nitride and has a thermal conductivity in therange of 140 W/mK to 200 W/mK.
 34. The reactor of claim 31, wherein thelift pin is comprised of one of sapphire and aluminum nitride.
 35. Thereactor of claim 34, wherein the opening through the body has a firstportion having a first diameter to support a head of the lift pin and asecond portion having a second diameter less than the first diameter.36. The reactor of claim 18, wherein the area to support a waferincludes a wafer pocket depressed in the surface of the stage and havingsidewalls disposed at an angle of approximately 60° to 80° relative to aplane perpendicular to the surface of the stage.
 37. A heating systemfor a chemical vapor deposition apparatus comprising: a resistive heatercomprising a stage including a surface having an area to support a waferand a body, a shaft coupled to the stage, a first heating elementdisposed within a first plane of the body of the stage, and a secondheating element disposed within a second plane of the body of the stage,the second plane of the body of the stare is a greater distance from thesurface of the stage than the first plane of the body; a firsttemperature sensor disposed within the shaft positioned to measure afirst temperature of the stage; and a power source coupled to the firstheating element and the second heating element.
 38. The system of claim37, wherein a power density of the first heating element is greater thana power density of the second heating element in an area correspondingwith the first portion of the area of the stage and the power density ofthe first heating element is less than power density of the secondheating element in an area corresponding with the second portion of thearea of the stage, wherein the stage body is substantially cylindricalsuch that a midpoint corresponds to an axis normal to the surface and afirst portion of the area of the stage is defined by a first radiusabout the axis and a second portion of the area is defined by a secondradius about the axis greater than the first radius.
 39. The system ofclaim 38, wherein the first heating element is disposed about the firstportion in a pair of coils and the first portion is defined by twosegments separated by a first axis, a first coil disposed in a firstsegment of the first portion and a second coil disposed in a secondsegment of the first portion, the first coil coupled to the second coilthrough the first axis, wherein the second heating element is disposedabout the second portion in a pair of coils and the second portion isdefined by two segments separated by a second axis, a first coildisposed in a first segment of the second portion and a second coildisposed in a second segment of the second portion, the first coilcoupled to the second coil through the second axis, and an intersectionof the first axis and the second axis defines an angle in a plane of thesurface between 0° and 180°.
 40. The system of claim 39, wherein theintersection of the first axis and the second axis defines an angle in aplane of the surface of at least 90°.
 41. The system of claim 38,further comprising a second temperature sensor positioned to measure asecond temperature corresponding to one of a first portion of the areaof the stage and a second portion of the area of the stage and a thirdtemperature sensor positioned to measure a third temperature in an areacorresponding to the other of the first portion of the surface area ofthe stage and the second portion of the surface area of the stage. 42.The system of claim 38, wherein the shaft of the heater has a portiondefining an interior opening through a length of the shaft, the systemfurther comprising a power source coupled to the first heating elementand the second heating element through the opening in the shaft.
 43. Thesystem of claim 38, further comprising a controller coupled to the powersource to control the temperature of the first heating element and thesecond heating element.
 44. The system of claim 43, wherein thecontroller controls the temperature of the first heating element and thesecond heating element to within ±2.5° C.
 45. The system of claim 44,wherein the controller is coupled to at least two of the firsttemperature sensor, the second temperature sensor, and the thirdtemperature sensor.
 46. The system of claim 45, wherein the firsttemperature sensor is a thermocouple and the second temperature sensorand the third temperature sensor are each a pyrometer.
 47. The system ofclaim 41, wherein the second temperature sensor is disposed in a firstwindow in the exterior surface of a chemical vapor deposition chamberand the third temperature sensor is disposed in a second window in theexterior surface of the chamber.
 48. The system of claim 47, furthercomprising a manifold coupled to the interior surface of the chamber todistribute process gases inside the chamber, the manifold positionedsuperiorly over the surface of the stage and having a thicknessapproximately three times the width of one of the first window and thesecond window.
 49. The system of claim 37, wherein the body of theheater has a bottom surface and a portion defining an opening throughthe body and substantially normal to the surface, the system furthercomprising: a lift pin having a first end and a second end, the firstend disposed within the opening through the body of the heater and thesecond end extending below the bottom surface of the body of the heater,a lift assembly coupled to the shaft to move the heater between a firstposition and a second position within reactor chamber; and a lift platecoupled to the lift assembly and having a portion disposed in thechamber, the portion disposed in the chamber including a surfaceextending in a direction normal to the shaft and substantially parallelto the top surface of the body of the stage, so that, when the heater isin the first position, the lift pin contacts the lift plate.
 50. Thesystem of claim 49, wherein the opening through the body has a firstportion having a first diameter to support a head of the lift pin and asecond portion having a second diameter less than the first diameter.51. A method comprising: supplying a power to a first resistive heatingelement disposed within a first plane of the body of a stage of aresistive heater and a second resistive heating element disposed withina second plane of the body of the stage; and varying a resistance of atleast one of the first resistive heating element and the secondresistive heating element in at least two areas of the stage.
 52. Themethod of claim 51, wherein the step of varying a resistance of at leastone of the first resistive heating element and the second resistiveheating element comprises providing the at least one resistive heatingelement with a first portion having at least a first resistance and asecond portion having at least a different second resistance.
 53. Themethod of claim 51, wherein the step of varying a resistance comprisesvarying a resistance of the first resistive heating element and aresistance of the second resistive heating element in at least two areasof the stage.
 54. The method of claim 51, wherein the resistive heatercomprises a stage including a surface having an area to support a waferand a body, the first heating element formed within a first plane of thebody of the stage, and a second heating element formed within a secondplane of the body of the stage, the second plane disposed at a greaterdistance from the surface area than the first heating element, the stepof varying the resistance further comprising: with the first heatingelement, providing a greater resistance in an area of the stage definedby a first radius from a midpoint than a second area defined by a secondradius from the midpoint greater than the first radius, and with thesecond heating element, providing a greater resistance in the secondarea than the first area.
 55. The method of claim 51, wherein theresistive heater comprises a stage including a surface having an area tosupport a wafer, the method further comprising: controlling thetemperature of the surface of the stage by regulating the power suppliedto the resistive heating elements.
 56. The method of claim 55, furthercomprising: measuring the temperature with at least two temperaturesensors, a first temperature sensor disposed within a shaft extendingfrom a bottom surface of the stage, the first temperature sensorpositioned to measure a first temperature of the stage and a secondtemperature sensor positioned to measure a second temperature in a firstarea of the stage defined by a first radius from a midpoint and a secondarea defined by a second radius from the midpoint; and comparing thetemperature measured by the first temperature sensor and the temperaturemeasured by the second temperature sensor.
 57. The method of claim 56,wherein the step of controlling the temperature comprises controllingthe compared temperature to within ±2.5° C. at temperatures around 750°C.
 58. A method comprising: providing a resistive heater in a chamber ofa reactor, the resistive heater comprising a stage disposed within thechamber including a surface having an area to support a wafer and abody, a first heating element having a first power density and a secondpower density, the first heating element formed within a first plane ofthe body of the stage, and a second heating element having a first powerdensity and a second power density, the second heating element formedwithin a second plane of the body of the stage, the second planedisposed at a greater distance from the surface than the first heatingelement; and supplying a power to the first heating element and to thesecond heating element.
 59. The method of claim 58, with the firstheating element, providing a greater power density in an area of thestage defined by a first radius from a midpoint than a second areadefined by a second radius from the midpoint greater than the firstradius, and with the second heating element, providing a greater powerdensity in the second area than the first area.
 60. The method of claim58, further comprising: controlling the temperature of the surface ofthe stage by regulating the power supplied to the resistive heatingelements.
 61. The method of claim 60, further comprising: measuring thetemperature with at least two temperature sensors, a first temperaturesensor disposed within a shaft extending from a bottom surface of thestage, the first temperature sensor positioned to measure a firsttemperature of the stage and a second temperature sensor positioned tomeasure a second temperature in a first area of the stage defined by afirst radius from a midpoint and a second area defined by a secondradius from the midpoint.
 62. The method of claim 60, the step ofcontrolling the temperature further comprising controlling thetemperature of the stage such that the second temperature measurementand the third temperature measurement are within ±3° C. at temperaturesaround 750° C.